This invention relates to a pilot-operated valve in general, and particularly to a valve for use in a refrigeration system which functions as a modulating valve and as a shut-off valve.
An evaporator pressure regulator is a back-pressure valve located between the evaporator and the compressor in the compressor suction line for controlling evaporator pressure at a relatively constant level in order to provide an approximate method of controlling cooling capacity of the refrigeration system. A refrigeration system back-pressure valve is disclosed in U.S. Pat. No. 3,303,664 which includes a main valve that is spring biased closed.
Any pressure drop in the suction line of a refrigeration system can be very detrimental to system efficiency; especially in low temperature systems where a pressure drop can considerably reduce the pumping efficiency of the compressor, and can also cause high discharge gas temperatures. Pressure drop in the suction line of a refrigerant system increases the electrical energy required to run the compressor at a given capacity. When a back-pressure valve is used in a suction line, it is important that only the minimum possible pressure drop occur across the valve in its full open position. It is therefore important that the valve be biased open so that suction line pressure is not required in order to overcome a closing spring bias force.
In multiple evaporator refrigeration systems, such as those commonly utilized in refrigerated cases for foods, it is desirable that individual evaporators be selectively shut-off so that they can be defrosted while at the same time other evaporators in the case remain in operation in order to maintain cool temperature in the refrigerated case. A valve which can function both as a modulating valve and as a shut-off valve can replace two individual valves for these purposes.